Field of the Invention
The present invention relates to a composite hollow fiber membrane and a manufacturing method thereof and, more particularly, to a composite hollow fiber membrane having improved water permeability and peel strength and a manufacturing method thereof.
Description of the Related Art
Separation methods for fluid treatment include a separation method using heating or phase change, a separation method using a filtration membrane, etc. A separation method using a filtration membrane is advantageous in that desired water quality may be stably acquired according to pore sizes of the filtration member and thus process reliability may be increased and manipulation, such as heating, etc., is not required due to use of the filtration membrane and thus such a separation method may be widely used in a separation process using microorganisms which may be influenced by heating.
Filtration membranes may be classified into flat sheet membranes and hollow fiber membranes according to shapes.
A hollow fiber membrane having a hollow formed therein has a much greater surface area than a flat sheet membrane and is thus advantageous in terms of water treatment efficiency. Hollow fiber membranes are widely used in microfiltration, such as manufacture of aseptic water, potable water and pure water, etc., and application thereof is now increased to sewage/wastewater treatment, solid-liquid separation in a septic tank, removal of suspended solids (SS) from industrial wastewater, filtration of river water, filtration of industrial water, filtration of swimming pool water, etc.
In order to apply a filtration membrane to water treatment, the filtration membrane should have excellent permeability and simultaneously have excellent pressure resistance and mechanical strength. However, a hollow fiber membrane has insufficient mechanical strength alone due to characteristics of a porous structure thereof. In order to increase mechanical strength of a hollow fiber membrane, trials to reinforce the hollow fiber membrane with a tubular braid have been executed.
For example, U.S. Pat. Nos. 7,909,177 and 8,201,485 respectively disclose composite hollow fiber membranes, each of which is manufactured by coating the outer surface of a tubular braid, serving as a support, with a polymer membrane.
In this documents, in order to increase a contact area between the tubular braid and the polymer membrane, the tubular braid is manufactured using thin multifilaments including monofilaments having fineness of 0.01 to 0.4 denier alone or by combining the thin multifilaments with other fabrics.
However, the tubular braid including the thin multifilaments has small pores and thus lowers water permeability of the composite hollow fiber membrane.
Moreover, the small pores of the tubular braid including the thin multifilaments prevent a polymer solution from permeating the tubular braid in the thickness direction thereof when the polymer membrane is formed. Consequently, improvement of peel strength between the tubular braid and the polymer membrane is limited.
Further, since the polymer solution does not permeate the tubular braid in the thickness direction thereof, the inner surface of the tubular braid becomes the inner surface of the composite hollow fiber membrane. The tubular braid has the non-uniform inner surface due to characteristics of the braid itself. The non-uniform inner surface of the tubular braid increases resistance to a fluid flow within the composite hollow fiber membrane, thus lowering water permeability of the composite hollow fiber membrane.